Antiphospholipid Syndrome (APS), also known as Hughes Syndrome, is a multiorgan vascular disease associated with myocardial infarction, stroke thrombosis and recurrent fetal loss. Forty- five percent of the people under the age of fifty who suffer strokes also demonstrate elevated levels of phospholipid antibody. Our hypothesis is that the presence of antiphospholipid antibodies in the circulation leads to vascular disorders, and that the escalating tissue damage can be abated with agents that bind the destructive antibodies. In order to test this hypothesis, it is necessary to create a genetically defined APS mouse that secretes antiphospholipid antibodies into the blood. We have produced and characterized a mouse monoclonal antibody which specifically recognizes phosphatidylserine. Preliminary data demonstrates that our monoclonal antibody binding specificity is similar to antibodies present in APS patients; this monoclonal antibody is therefore appropriate to develop a treatment model. The heavy and light chain of our monoclonal antiphospholipid antibody will be cloned by RT-PCR. These cDNAs will include the endogenous secretory peptide signal sequence. Bigenic mice will be used to direct ligand induced expression in the liver. Each monoclonal immunoglobulin chain will be differentially tagged with HA or FLAG epitopes. The transgenic animals will be characterized and compared with normal animals for the hallmark symptoms of APS, including prolonged in vitro coagulation times, recurrent fetal loss and vascular disease. An additional goal of this proposal is to develop treatment strategies for APS. Our approach is to neutralize the disease-causing antibodies. Peptides which bind and block the monoclonal antiphospholipid antibody in vitro can be selected from a combinatorial phage-display library of random peptides. Isolated peptides will be assessed for the ability to reduce the symptoms of APS displayed by this transgenic mouse. This study will produce a genetically-defined mouse model of APS which will prove useful for developing treatment strategies to ameliorate the symptoms associated with APS.